Global Variables

Focus default_focus

Variable

Effectively, the default Focus in Picture::output().
See Picture Reference; Outputting; Functions.
It's not really the default, but the version of
output() that doesn't take a
Focus argument calls another version
that does take one, passing default_focus to the
latter as its Focus argument.

It's necessary to do this in such a roundabout way,
because Picture::output() must be declared before
class Focus is completely defined and default_focus is declared.

The declaration Focus& f = default_focus; makes f a
reference to default_focus, i.e., it makes f another name
for default_focus. This may be convenient, if you don't feel
like typing default_focus.